1. Technical Field
This invention relates to linear light-emitting diode (LED) lamps that work with any linear tube lamp fixtures configured as single-ended or double-ended, and more particularly to a universal, shock and fire hazard-free linear LED tube lamp with a shock-protection mechanism.
2. Description of the Related Art
Solid-state lighting from semiconductor light-emitting diodes (LEDs) has received much attention in general lighting applications today. Because of its potential for more energy savings, better environmental protection (with no hazardous materials used), higher efficiency, smaller size, and longer lifetime than conventional incandescent bulbs and fluorescent tubes, the LED-based solid-state lighting will be a mainstream for general lighting in the near future. Meanwhile, as LED technologies develop with the drive for energy efficiency and clean technologies worldwide, more families and organizations will adopt LED lighting for their illumination applications. In this trend, the potential safety concerns such as risk of electric shock and fire become especially important and need to be well addressed.
In a retrofit application of a linear LED tube (LLT) lamp to replace an existing fluorescent tube, one must remove the starter or ballast because the LLT lamp does not need a high voltage to ionize the gases inside the gas-filled fluorescent tube before sustaining continuous lighting. LLT lamps operating at the AC mains, such as 110, 220, and 277VAC, have one construction issue related to product safety and needed to be resolved prior to wide field deployment. This kind of LLT lamps always fails a safety test, which measures through lamp leakage current. Because the line and the neutral of the AC mains apply to both opposite ends of the tube when connected, the measurement of current leakage from one end to the other consistently results in a substantial current flow, which may present a risk of shock during re-lamping. Due to this potential shock risk to the person who replaces LLT lamps in an existing fluorescent tube fixture, Underwriters Laboratories (UL) uses its standard, UL 935, Risk of Shock During Relamping (Through Lamp), to do the current leakage test and to determine if LLT lamps under test meet the consumer safety requirement.
Appliances such as toasters and other appliances with exposed heating filaments present the same kind of hazard. When the line and the neutral wire reverse, the heating filaments can remain live even though the power switches to “off”. Another example is screw-in incandescent bulbs. With the line and the neutral wire reversed, the screw-in thread of the socket remains energized. These happen when the line and the neutral wires in the wiring behind the walls or in the hookup of sockets are somehow interchanged even with polarized sockets and plugs that are designed for safety. The reason why a consumer can widely use the appliances with heating filaments and screw-in light lamps without worrying about shock hazard is that they have some kinds of protections. The said appliances have protection grids to prevent consumers from touching the heating filaments even when they are cool. The screw-in light lamp receptacle has its two electrical contacts, the line and the neutral in proximity, recessed in the luminaire. When one screws an incandescent bulb in the receptacle, little shock risk exists.
As mentioned, without protection, shock hazard will occur for an LLT lamp, which is at least 2 feet long; it is very difficult for a person to insert the two opposite bi-pins at the two ends of the LLT lamp into the two opposite sockets at two sides of the linear tube lamp fixture at the same time. Because protecting consumers from possible electric shock during re-lamping is a high priority for LLT lamp manufacturers, they need to provide a basic protection design strictly meeting the minimum leakage current requirement and to prevent any possible electric shock that users may encounter in actual usage, no matter how they instruct a consumer to install an LLT lamp in their installation instructions.
Referring to FIGS. 1 and 2, a conventional LLT lamp 100 comprises a housing 110 with a length much greater than its diameter of 25 to 32 mm, two end caps 120 and 130 with bi-pins 180 and 190 respectively on two opposite ends of the housing 110, LED arrays 140 mounted on a printed circuit board (PCB) 150, and an LED driver 160 used to receive energy from the AC mains through electrical contacts 142 and the bi-pins 180 and 190, to generate a proper DC voltage with a proper current, and to supply it to the LED arrays 140 such that the LEDs 170 on the PCB 150 can emit light. The bi-pins 180 and 190 on the two end caps 120 and 130 connect electrically to the AC mains, either 110 V, 220 V, or 277 VAC, through two electrical sockets located lengthways in an existing fluorescent tube fixture whereas the two sockets in the fixture connect electrically to the line and the neutral wire of the AC mains, respectively. This is a so called “double-ended” configuration.
To replace a fluorescent tube with an LLT lamp 100, one inserts the bi-pin 180 at one end of the LLT lamp 100 into one of the two electrical sockets in the fixture and then inserts the other bi-pin 190 at the other end of the LLT lamp 100 into the other electrical socket in the fixture. When the line power of the AC mains applies to the bi-pin 180 through one socket, and the other bi-pin 190 at the other end has not yet been in the other socket in the fixture, the LLT lamp 100 and the LED driver 160 are deactivated because no current flows through the LED driver 160 to the neutral. However, the internal electronic circuitry is live. At this time, if the person who replaces the LLT lamp 100 touches the exposed bi-pin 190, which is energized, he or she will get electric shock because the current flows to earth through his or her body—a shock hazard.
Almost all the LLT lamps currently available on the market are without any protections for such electric shock. The probability of getting shock is 50%, depending on whether the person who replaces the lamp inserts the bi-pin first to the line of the AC mains or not. If he or she inserts the bi-pin 180 or 190 first to the neutral of the AC mains, then the LLT lamp 100 is deactivated while the internal circuitry is not live—no shock hazard. An LLT lamp supplier may want to adopt single protection only at one end of an LLT lamp in an attempt to reduce the risk of shock during re-lamping. However, such a single protection approach cannot completely eliminate the possibility of shock risk. As long as shock risk exists, the consumer product safety remains the most important issue.
An easy solution to reducing the risk of shock is to connect electrically only one of two bi-pins at the two ends of an LLT lamp to the AC mains, leaving the other dummy bi-pin at the other end of the LLT lamp insulated, so called “single-ended”. In such a way, the line and the neutral of the AC mains go into the LLT lamp through the single-ended bi-pin, one for “line” (denoted as L, hereafter) and the other for “neutral” (denoted as N, hereafter). The electrically insulated dummy bi-pin at the other end only serves as a lamp holder to support LLT lamp mechanically in the fixture. In this case, however, the retrofit and rewiring of the existing fixture to enable such LLT lamp may involve two new electrical sockets replacement in the fixture and needs much longer time to complete the rewiring because conventional fluorescent tube is double-ended, and its fixture and lamp holder sockets are wired in a double-ended manner. The new sockets, rewiring, and installation costs together will be too high for consumers to replace conventional fluorescent tubes economically. Therefore, some manufacturers have modified the dummy bi-pin by internally connecting the two pins with a conductor. The purpose is to convert a double-ended fixture/wiring into a single-ended configuration so that the single-ended LLT lamp can be used in the double-ended fixture/wiring as shown in FIG. 3, no matter whether the active end of the LLT lamp is on the left or right hand side in the fixture.
In FIG. 3, the AC mains supply voltage to the bi-pin sockets in the lamp holder 311 and 312 from two opposite ends of the LLT lamp 101—a double-ended configuration. However, LLT lamp 101 is internally connected as single ended because two pins 181 and 182 of the bi-pin are at one end, from which the LED driver 400 receives energy to power LED arrays 214. The conductors 255 in the sockets of the lamp holder 311 and 312 are used to connect the bi-pins to the AC mains through electrical contacts shown as dots. The “dot” notation will be used to indicate electrical contacts throughout the figures. In order to receive energy from both ends of a double-ended fixture so that such a single-ended LLT lamp can operate in the double-ended fixture, manufacturers interconnect the two pins 183 and 184 of the bi-pin at one end with a conductor 251 inside the lamp such that electric current can flow through the pin 183, the conductor 251, the pin 184, and an electrical wire 252 to the pin 182 at the other end. The modification seems to work to operate the LLT lamp in the double-ended fixture and be able to pass UL leakage current test. But this introduces shock and fire hazards. Imagine what will happen if consumers insert this electrically shorted end to a real single-ended fixture that has L and N connections on the bi-pin socket. This definitely will burn the connections on the bi-pin, possibly causing fire, and trip the circuit breaker. Due to this potential shock and fire risk for this kind of LLT lamp modification used with an existing fluorescent tube fixture, UL requires that the lamp base bi-pin used for mechanical support only not be interconnected or connected to dead metal parts of the lamp base. Furthermore, such single-ended LLT lamps are subjected to the requirements in UL Isolation of Lamp Pins test, ensuring no indication of fire or risk of electric shock if manufacturers want their products to be UL certified.
Similar hazards occur for double-ended lamps. There are many double-ended lamps without shock-protection mechanisms on the linear LED lighting market. Such lamps will never pass UL leakage current test and present the shock risk during re-lamping, as mentioned above. In addition, such non-UL compliant LLT lamps have their bi-pins internally connected. In FIG. 4, the LED driver 400 receives energy from both bi-pin sockets in the lamp holders 313 and 314 at opposite ends of the LLT lamp 102 to power LED arrays 214—a double-ended configuration. The two pins 181 and 182 at one end are internally interconnected with a conductor 253. Similarly, the two pins 183 and 184 at the other end are internally interconnected with a conductor 254. In this case, as long as either one electrical contact in the bi-pin sockets has a power, the LLT lamps can operate. Manufacturers do this modification just trying to make it easy for consumers to more easily retrofit their linear tube lamp fixtures without considering that the same hazards as mentioned for the single-ended LLT lamps may occur if either one of such bi-pins is inserted into a powered socket in a single-ended fixture with single-ended wiring. Furthermore, because LLT lamps have a very long service life, consumers who do not know single-ended and double-ended configurations may try to install their LLT lamps in another fixture with unknown wiring configuration several years later while original installation/wiring instructions may not be found. In this case, there exist fire and shock hazards.
In the U.S. Pat. No. 8,147,091, issued Apr. 3, 2012, double shock protection switches are used in a double-ended LLT lamp to isolate its LED driver such that a leakage current flowing from a live bi-pin, through the LED driver, to an exposed bi-pin is eliminated without hazards. FIGS. 5 and 6 illustrate an LLT lamp with such shock protection switches. The LLT lamp 200 has a housing 201; two lamp bases 260 and 360, one at each end of the housing 201; two actuation mechanisms 240 and 340 of shock protection switches 210 and 310 in the two lamp bases 260 and 360, respectively; an LED driver 400; and LED arrays 214 on an LED PCB 205.
FIG. 6 is a block diagram of an LLT lamp 200 with the protection switches 210 and 310. The shock protection switch 210 comprises two electrical contacts 220 and 221 and one actuation mechanism 240. Similarly, a shock protection switch 310 comprises two electrical contacts 320 and 321 and one actuation mechanism 340. The electrical contact 220 in the protection switch 210 connects electrically to the bi-pin 250 that connects to the L wire of the AC mains, and the other contact 221 connects to one of the inputs 270 of the LED driver 400. Similarly, the electrical contact 320 in the protection switch 310 connects electrically to the bi-pin 350 that connects to the N wire of the AC mains, and the other contact 321 connects to the other input 370 of the LED driver 400. The switch is normally off. Only after actuated, will the switches turn “on” such that they connect the AC mains to the LED driver 400 that in turn powers the LED arrays 214. Served as gate controllers between the AC mains and the LED driver 400, the protection switches 210 and 310 connect the line and the neutral of the AC mains to the two inputs 270 and 370 of the LED driver 400, respectively. If only one shock protection switch 210 is used at one lamp base 260, and if the bi-pin 250 of this end happens to be first inserted into the live socket at one end of the fixture, then a shock hazard occurs because the shock protection switch 210 already allows the AC power to electrically connect to the LED driver 400 inside the LLT lamp when the bi-pin 250 is in the socket. Although the LLT lamp 200 is deactivated at the time, the LED driver 400 is live. Without the shock protection switch 310 at the other end of the LLT lamp 200, the LED driver input 370 connects directly to the bi-pin 350 at the other end of the LLT lamp 200. This presents a shock hazard. However, if the shock protection switch 310 is used in accordance with this application, the current flow to the earth continues to be interrupted until the bi-pin 350 is inserted into the other socket, and the protection switch 310 is actuated. The switch redundancy eliminates the possibility of shock hazard for a person who installs an LLT lamp in the existing fluorescent tube fixture.
Double shock protection switches used in a double-ended LLT lamp can be used to isolate its LED driver such that a leakage current flowing from a live bi-pin, through the LED driver, to an exposed bi-pin is eliminated without hazards. However, such lamps are non-operable because no power supplies to the LED driver when used with single-ended fixtures. Even worse, when the two adjacent pins of the bi-pin on either one of the two ends in the double-ended LLT lamp are abnormally interconnected, the lamps may present a fire hazard when installed in the single-ended fixture, as mentioned above. In the present invention, however, double shock protection switches are used in a universal single-ended or double-ended LLT lamp to isolate its degenerate voltage sensing and control mechanism such that the leakage current flowing from a live bi-pin, through the degenerate voltage sensing and control mechanism and an LED driver, to an exposed bi-pin is interrupted without hazards.